In some devices such as disc drives, a voice coil motor (VCM) is used to position at least one transducer head over a desired radial position on at least one disc that stores information. A VCM may include a first plate, and may include a second plate spaced from the first plate. A permanent magnet is joined to the first plates to form an air gap. Where two plates are provided, the upper plate and any attached permanent magnets is referred to as a top pole assembly and the lower plate and any attached magnets is referred to as a bottom pole assembly. A voice coil is positioned in the air gap and is rotationally mounted to an axle. Each transducer head is mounted on an arm which forms part of an actuator that is coupled to the voice coil. When electric current is passed through the voice coil, the current interacts with the magnetic field in the air gap. This causes movement of the voice coil, which in turn effects rotation of the actuator.
When the disc drive is energized and the disc is spinning, the voice coil motor positions the head over data stored on the spinning disc. The spinning generates an air bearing separating the head from the spinning disc. When the disc drive is de-energized and the disc stops spinning, there is no air bearing and the head contacts the smooth stationary disc. If the sticking friction (“stiction”) between the head and the disc is too great, the spindle motor may be incapable of rotating the disc when the disc drive is restarted. A common method of avoiding this problem is to move the head with the voice coil motor to a “park” portion of the disc when the disc drive is de-energized. The park portion of the disc is textured so that it will not stick to the head, and no data is stored on the park portion. Various kinds of latches may be used to latch the actuator in this park position when the disc drive is de-energized. To ensure that the actuator remains in the park position even when the disc drive experiences a high level of shock, in addition to a primary latch, a secondary or inertial latch may also be employed. Inertial latches move in response to high level external shocks to lock the actuator in place and thereafter disengage when the shock level decreases. Under lower levels of shock, which are insufficient to move the inertial latch, the actuator is held in place only by the primary latch.
One problem faced by drive manufacturers is the cost incurred by additional parts and assembly steps required to install these latches. For example, one installation method involves mounting the inertial latch to one of the top and bottom pole assemblies of the VCM prior to disc drive assembly. In this instance, the combined inertial latch and single (top/bottom) pole are transported from a supplier to the disc drive manufacturing plant and/or along an assembly line during manufacture of the disc drive before the top and bottom poles of the VCM are joined together. Thus, the inertial latch needs to be constrained on the single (top/bottom) pole during transportation. One current technique to constrain the inertial latch on the top/bottom pole involves the use of a pivot pin with a cap. The pivot pin passes through a first groove in a hub of the inertial latch and fits into a second groove in the top/bottom pole of the VCM. The cap of the pivot pin constrains the inertial latch on the top/bottom pole of the VCM. One of the disadvantages of this technique is that pivot pins with caps are costly. Further, the inertial latch has to be first mounted on the pin and then the pin with the mounted inertial latch has to be press-fit into the upper/lower plate of the VCM. This is a multi-step operation which is relatively time consuming.
Embodiments of the present invention provide solutions to these and other problems, and offer other advantages over the prior art.